The known antibiotic nogalamycin, and a process for its preparation, are described in U.S. Pat. No. 3,183,157. The structure of nogalamycin can be shown as follows: ##STR1##
Antibiotics nogalarol and nogalarene, produced by acid hydrolysis of nogalamycin, and o-methylnogalarol, produced by acidic methanolysis of nogalamycin or nogalarol, are disclosed in U.S. Pat. No. 3,501,569.
Nogalamycinic acid is prepared by chemical modification of nogalamycin. The structure of nogalamycinic acid is as follows: ##STR2##
Nogalamycinic acid can be converted to nogamycin by contacting it with dimethylformamide. Nogamycin has the following structural formula: ##STR3##
U.S. Pat. No. 4,086,245 concerns 7-O-alkylnogarols an their preparation from nogamycin. It is now known that these compounds are the (R) form and, that, also produced in the process, but heretofore not recognized or recovered, are the compounds of the subject invention which are the (S) form. The compounds of U.S. Pat. No. 4,086,245 can be shown as follows: ##STR4## wherein R is an alkyl group of from 1 to 4 carbon atoms, inclusive.